This invention relates to medical treatment of relatively deeply seated tissue using optical radiation.
Laser radiation has been widely used in medicine for performing surgical procedures or treating tissue. Laser radiation has been applied both extra-corporeally, to treat skin tissue, and intra-corporeally to treat venous or arterial walls, walls in the gastro-intestinal tract, or for the removal of plaque located on the arterial walls. The laser light has been used also for coagulation of surface wounds. Advantages of the laser light arise from the ability of delivering specific energy to the targeted, localized tissue.
Depending on the wave length of the radiation, a large amount of radiation can penetrate deeper into the tissue, but still a significant portion of the radiation is absorbed by the surface layers of the tissue. The surface absorption limits the intensity of radiation used in the tissue treatment due to the thermal damage to the surface tissue at high intensities.
Selective delivery of the laser radiation is also used as a catalyst for photochemical reactions such as in photodynamic therapy. In photodynamic therapy, a patient is injected with a drug that is designed to selectively treat certain tissues such as cancerous tissue. The drug is delivered in an inert state and is activated by light of a certain wavelength. The activated drug is limited only to the irradiated tissue which substantially eliminates possible adverse affects on other non-targeted tissue.
Laser radiation has also been used for ablating and removing specific tissue. In treatment of benign prostatic hyperplasia, the ablation process removes a portion of an enlarged prostate; this relieves the obstructive symptoms associated with the enlarged prostate. In the treatment process, the laser light heats the tissue to about 100.degree. C. until the irradiated tissue is destroyed, and the destroyed tissue is later discharged from the body.
In treatment of ventricular tachycardia (i.e., disorder of electrical control signals within the heart), the laser light is used to target and destroy specific myocardial tissue in order to remedy the irregularity of the electrical signals. Based on detailed electro-physiological mapping of the myocardial tissue, by destroying the tissue that carries the abnormal electrical signals, the normal rhythm is restored.
In the above-described procedures, named as some examples, it is necessary to irradiate, with a sufficient dose of light, tissue located below surface accessible by external laser radiation. Due to relatively large doses of light needed for the treatment, in many cases the treatment of the below surface tissue has been difficult since the surface tissue is damaged in the process.